This invention relates generally to a strain gauge and is concerned more particularly with a portable strain gauge for measuring the stress in bars.
Conventional strain gauges whether electrical or mechanical, are characterized by a number of disadvantages as to cost, maintenance, complexity, and accuracy after prolonged use. In addition, the proper attachment of existing strain gauges to the specimens that are to be measured involves considerable time and difficulty, and this makes them unsatisfactory in situations where quick attachment and detachment is necessary or desirable.
One such situation is frequently encountered in the pressure molding industry, particularly die casting and plastic molding. The dies or molds are held tightly closed by metal platens which are moved together by a toggle linkage system that includes four tie bars. These tie bars receive the entire force that locks the dies or molds together, and it is extremely important to assure that the locking force is distributed equally among the tie bars in order to avoid excessive wear and damage to the expensive locking mechanism. Therefore, it is necessary to use a strain gauge to measure the stress on each tie bar so that appropriate adjustments can be made to equalize the stress on the tie bars. As previously indicated, the instruments presently available for this purpose are not only expensive to manufacture and maintain, but also require excessive time to attach to and detach from each of the tie bars.
Accordingly, there is a need for a strain gauge that is economical, easily operated, and quickly attached to and detached from the bars that are to be measured. It is the primary goal of the present invention to fulfill this need.
More specifically, it is an object of the invention to provide a strain gauge that may be quickly and easily attached to a bar and detached therefrom. This important object is achieved through the use of magnetic mounting bases that are able to adhere directly to steel bars. The invention further contemplates the use of mounting pads which may be strapped to the bar and which adhere to the magnetic bases in situations where the bar itself is not able to be magnetically attracted to the bases.
Another object of the invention is to provide a strain gauge that operates to mechanically convert the deformation or strain of a bar directly into an accurate read-out of the stress on the bar.
A further object of the invention is to provide a strain gauge of the character described in which a standard commercially available dial indicator is incorporated without requiring further modification.
Still another object of the invention is to provide a strain gauge of the character described in which the operating mechanism is protected against excessive forces and wear during use.
An additional object of the invention is to provide a strain gauge of the character described that includes a lock for holding the operating mechanism in place between uses in order to protect it against damage.
Yet another object of the invention is to provide a strain gauge of the character described in which the operating components are easily accessible for adjustment, inspection and repair.
A still further object of the invention is to provide a strain gauge of the character described that is economical to manufacture, simple to use, and accurate and reliable in operation even after extensive use.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawings.